The invention relates to a sintering apparatus for sintering at least one workpiece, in particular a dental workpiece, with a sintering chamber for receiving the workpiece to be sintered during the sintering operation, wherein the sintering chamber is delimited by a base area of the sintering apparatus on which the workpiece can be placed during the sintering operation, wherein the sintering apparatus has at least one gas feed for introducing protective gas into the sintering chamber. The invention also relates to a method for sintering at least one workpiece, in particular a dental workpiece, in a sintering apparatus and also to an arrangement with at least one workpiece, in particular a dental workpiece, to be sintered and a sintering apparatus.
For the sintering of workpieces, in particular dental workpieces, a wide variety of sintering apparatuses have already been proposed in the prior art. DE 20 2011 106 734 U1 discloses a sintering chamber in which a slight negative pressure is intended to be produced in the upper region of a sintering space by a Venturi effect. In DE 20 2011 005 465 U1, it is proposed for example to lower the workpieces to be sintered in an annular sintering tray completely within sintering granules, so that the sintering granules completely surround and cover the workpieces to be sintered during the sintering operation. It has been found from practical experience that, with this arrangement, the process of shrinkage of the workpiece that occurs during the sintering operation may be hindered, which leads to unwanted deformation of the workpiece. A sintering apparatus of the generic type is also disclosed for example in WO 2011/020688 A1. In this document it is proposed that a quartz tray, which has the base area, should be filled during the operation of the sintering apparatus with inert beads, into which the article to be sintered is placed. To enter the quartz tray, that is to say the area around the workpiece to be sintered, the protective gas must flow around the quartz tray in order to enter the interior of the quartz tray from above. It has been found that, with this type of arrangement, a relatively great amount of protective gas is consumed during the sintering operation and impairments of the article to be sintered can nevertheless be caused by remains of another gas, in particular oxygen.
In DE 10 2011 056 211, it is proposed to cover the tray in which the article to be sintered is located by a closure element, wherein the covered tray can be flowed through by protective gas or inert gas. However, it is not explained in this document what form the covered tray should take to allow a flow to pass through it in this way.
DE 10 2009 019 041 A1 concerns a sintering apparatus for sintering magnesium or magnesium alloys at relatively low sintering temperatures of 600° C. to 642° C. under a protective gas atmosphere. In FIG. 5 of this document, it is proposed to pass any impurities of the gas in the outer region of the crucible through getter material before this impurity can get into the inner region of the crucible.
Extensive tests with a wide variety of sintering apparatuses have shown that even small changes in the structure of arrangements and sintering apparatuses of the generic type can often have an unexpectedly strong influence on the quality of the sintering result, in particular at very high sintering temperatures of sometimes over 1200° C. In particular, it is difficult with arrangements known in the prior art to ensure that no undesired discoloration or oxidation of the workpiece to be sintered occurs.